The present invention relates generally to the field of electrosurgery and, more particularly, to surgical devices and methods which employ high frequency electrical energy to cut, ablate, resect, coagulate, or otherwise modify target tissue. The present invention also relates to apparatus and methods for volumetrically removing tissue from a target site by a cool ablation (Coblation®) procedure involving molecular dissociation of tissue components, and for electrosurgically resecting one or more fragments of target tissue for biopsy.
The field of electrosurgery includes a number of loosely related surgical techniques which have in common the application of electrical energy to modify the structure or integrity of patient tissue. Electrosurgical procedures usually operate through the application of very high frequency currents to cut or ablate tissue structures, where the operation can be monopolar or bipolar. Monopolar techniques rely on external grounding of the patient, where the surgical device defines only a single electrode pole. Bipolar devices comprise both an active electrode and a return electrode for the application of current between their surfaces.
Conventional electrosurgical methods generally reduce patient bleeding and trauma associated with tissue cutting operations and improve the surgeon's visibility. These electrosurgical devices and procedures, however, suffer from a number of disadvantages. For example, monopolar electrosurgery methods generally direct electric current along a defined path from the exposed or active electrode through the patient's body to the return electrode, which is externally attached to a suitable location on the patient's skin. In addition, since the defined path through the patient's body has a relatively high electrical impedance, large voltage differences must typically be applied between the active and return electrodes to generate a current suitable for cutting or coagulation of the target tissue. This current, however, may inadvertently flow along localized, non-defined pathways in the body having less impedance than the defined electrical path. This situation will substantially increase the current flowing through these non-defined paths, possibly causing damage to or destroying tissue along and surrounding such pathways.
Another limitation of conventional bipolar and monopolar electrosurgery devices is that they are not suitable for the precise removal (ablation) of tissue. For example, conventional electrosurgical cutting devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” along the pathway of localized tissue heating. The tissue is parted along the pathway of vaporized cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site.
In addition, conventional electrosurgical methods are generally ineffective for ablating certain types of tissue, and in certain types of environments within the body. For example, loose or elastic connective tissue, such as the synovial tissue in joints, is extremely difficult (if not impossible) to remove with conventional electrosurgical instruments because the flexible tissue tends to move away from the instrument when it is brought against this tissue. Since conventional techniques rely mainly on conducting current through the tissue, they are not effective when the instrument cannot be brought adjacent to or in contact with the elastic tissue for a long enough period of time to energize the electrode and conduct current through the tissue.
In an effort to overcome at least some of these limitations of electrosurgery, laser apparatus have been developed for use in arthroscopic and other procedures. Lasers do not suffer from electrical shorting in conductive environments, and certain types of lasers allow for very controlled cutting with limited depth of necrosis. Despite these advantages, laser devices suffer from their own set of deficiencies. Firstly, laser equipment can be very expensive because of the costs associated with the laser light sources. Moreover, those lasers which permit acceptable depths of necrosis (such as eximer lasers, erbium:YAG lasers, and the like) provide a very low volumetric ablation rate, which is a particular disadvantage in cutting and ablation of fibrocartilage, articular cartilage, and meniscal tissue. The holmium:YAG and Nd:YAG lasers provide much higher volumetric ablation rates, but are much less able to control depth of necrosis than are the slower laser devices. The CO2 lasers provide high rates of ablation and low depth of tissue necrosis, but cannot operate in a liquid-filled cavity.
Bipolar electrosurgical devices have an inherent advantage over monopolar devices in that the return current path does not flow through the patient beyond the immediate site of application of the bipolar electrodes. Thus, bipolar electrosurgery avoids inadvertent stimulation of nerves and nerve damage in the general vicinity of the treatment site. Avoidance of nerve damage is of importance, for example, when targeting tissue such as the prostate gland, where damage to surrounding nerves could result in impotence and/or incontinence.
Conventional, monopolar electrosurgical techniques have favored use of non-conductive (electrolyte-free) media, such as glycine solution, as an irrigant and distension medium at the target site. However, electrolyte-free media have the disadvantage of potentially causing adverse physiological effects in the form of water intoxication, for example, if glycine solution enters the circulation via a severed vein. Such water intoxication is due to dilution of serum sodium by the electrolyte-free medium. Bipolar electrosurgical apparatus and methods, according to the present invention, allow the use of isotonic saline as irrigant and distension medium, thereby eliminating problems related to water intoxication of the patient.
The instant invention provides improved apparatus, systems, and methods for the electrosurgical ablation and cutting of tissue. These systems and methods are capable of selectively cutting and ablating tissue in a precisely controlled manner, with little or no damage to non-target tissue.